1. Field of the Invention
This invention relates to an apparatus and method for diagnostic machines in a production line. More particularly, this invention relates to analyzing critical points in production line machines.
2. Description of the Prior Art
Many industrial production lines are comprised of a plurality of processing machines which are tied together. One example is an industrial production line for producing corrugated paper. Corrugated paper is generally produced by using three webs of paper. One web is fluted (the flute) and is glued between two other flat webs of paper. This process can be done using anywhere from 5 to 25 different machines which are mechanically and electrically coupled to one another.
All of the machines used to produce corrugated paper are collectively called a corrugator. A corrugator can be 300 feet long or longer. At one end, paper enters the corrugator from large rolls which are nominally 8 feet wide. The three webs of paper (including the flute) are then glued together, sheared, slitted and scored, and cut to the proper length. Finally, the paper is stacked.
Usually, corrugators are made up of dual machines which can run two or more orders at the same time. Since the paper rolls generally come in 8 foot wide rolls, several orders are set up to best utilize that dimension. For example, one order requiring six foot wide sheets of corrugated paper is run along with an order requiring two foot wide sheets. After being glued, the paper is slit to the proper width. Therefore, it is economically efficient to run more than one order at the same time.
The machines in a corrugator come from a wide variety of vendors and are not precisely matched. Sometimes machines are all manufactured by the same vendor. Corrugators typically run at a speed of approximately 600 feet of paper per minute and the paper tension in the corrugator is important for proper production. Since the machines run at a high rate of speed and since proper paper tension is important throughout the corrugator, the machines must be synchronized with one another.
Also, each machine has its own individual safety interlocks. Since the operation of the entire corrugator depends on the operation of each individual machine in the corrugator, when one machine is shut down by a safety interlock, the other machines should also be shut down. Therefore, the electrical interlocks of the machines are tied to one another so that all machines stop when one interlock is tripped.
Typically, a corrugator takes a crew of 5 members to operate. Each crew member operates one portion of the corrugator. When a problem exists in one machine in the corrugator, a safety interlock may shut that machine off or the operator may push a stop button. When this happens, the entire corrugator is shut down.
When a safety interlock stops a corrugator, confusion among the crew members results because none of them knows which machine has stopped the corrugator or what caused the stop. This can result in what should have been a 30 second stop turning into a ten minute or longer stop which substantially decreases production. For example, where the corrugator is running at 600 ft/min., nine extra minutes of downtime means a loss of more than one mile of corrugated paper production.
When one of the operators pushes a stop button, the corrugator usually coasts to a stop. While the corrugator is coasting, a second problem can arise (such as a jam in one of the machines). The operator of the jammed machine will think that the jam is the problem which caused the corrugator to stop initially. Upon clearing the jam, the operator will restart the corrugator not realizing that the initial condition which stopped the corrugator was that another operator pressed a stop button. This also results in confusion and time delays in getting the corrugator running again.
Another problem which causes the corrugator to stop is an intermittent problem. For example, a relay contact can temporarily open up causing the corrugator to stop but while the corrugator is coasting to a stop, the relay contact could automatically reset itself. Machines in the corrugator don't stop at the same rate, so during the time the corrugator is coasting to a stop, another problem may arise. The operator will see the apparent problem and erroneously determine that it caused the corrugator to stop initially. The intermittent problem having temporarily remedied itself, the corrugator will be restarted and the intermittent problem will never be identified. However, if the intermittent problem is recurring, the corrugator stoppages can be very timely and costly. Typically, corrugators are in dusty, extremely humid and hot environments which contribute to causing intermittent component failures.
Because of the large number of machines (typically from different vendors) and the intertwined safety interlocks involved in a corrugator, finding the exact problem which caused the corrugator to stop running can be very difficult. Each of the different machines has many operator's manuals, schematics and other diagrams which are used to fix the machines. Therefore, when the corrugator stops and the crew does not know which machine has caused the stop, it can take a repairman or serviceman minutes, hours or even days to wade through the necessary documentation to find the problem. Since the corrugated paper industry usually strives for "just-in-time" operation, these delays in finding problems are very expensive.
Another problem which causes corrugators to stop running is that jams can occur when the corrugator shifts from producing corrugated paper for one order to producing another dimension or another quality of corrugated paper for another order. These order changes require adjustments in various machines in the corrugator. When the order change begins and the adjustments have not been made, machine jams and other problems can result in corrugator stoppage. These stoppages are extremely costly in a short order plant where small quantity orders are produced. Corrugators in this type of plant may typically run for only 4 or 5 minutes between order changes. With no warning as to the problems that accompany the order change, operators cannot make the necessary adjustments in time and corrugator downtime is drastically increased.
Until now, manufacturers in the corrugated paper industry have concentrated on making each of the individual machines in the corrugator more technically advanced. However, as yet, no one has addressed the problem of finding the reasons that these highly automated machines fail, fixing the problems and restarting the machines. Therefore, some of the major costs in the corrugated paper industry are those costs which are associated with downtime of the corrugator. One of the primary costs is lost business. The just-in-time nature of the corrugated paper industry requires producers to supply orders on very short notice. If the corrugator is down for a period of hours or days, corrugated paper purchasers will take their business elsewhere.
Another major cost is overtime payments. When the corrugator is down, in order to provide the purchasers with the corrugated paper they have ordered, the producers must run overtime to make up for the corrugator downtime. Yet another cost is the cost of repair and service personnel which are required to find the problems in the corrugator. Due to the complex nature of the machines in the corrugator, it can take service and repair persons weeks to find the problem. All this time will be charged to the producer and that can be very costly.
Several existing diagnostic systems are on the market today. However, they generally simply tie into the programmable controllers of each of the machines in a production line. Therefore, they only provide the diagnostics capability which the programmable controller in each machine provides in the first place if it provides any at all. None of them are able to isolate problems which cause stoppage of the production line down to a component level.
Also, the diagnostic systems on the market today do not provide an operator with the cause of a current downtime period along with a most critical condition keeping the production line from being restarted.